Accurate assessment and tracking of infant body composition is useful for evaluating the amount and quality of weight gain, which can provide key information in both clinical and research settings. Thus, body composition analysis (BCA) results can be used to monitor and evaluate infant growth patterns, efficacy of nutritional and medical interventions, progression of chronic disease, and recovery from malnutrition. The collection of infant body composition data can also be used to establish normative databases and help create generalized resting energy expenditure prediction formulas for infants. These formulas can then be used to accurately measure energy expenditure in infants, which has important implications in the determination of optimal energy requirements, especially in preterm infants. Most importantly, because of the significant association between early infant development and childhood obesity and in light of the phenomenal increase in the prevalence of childhood obesity in the United States and worldwide, BCA during infancy has the potential to become an important research and diagnostic tool for the study and prevention of child and adult obesity. However, the methods that are currently available to researchers and clinicians, such as isotope dilution, dual energy x-ray absorptiometry, air-displacement plethysmography, total-body electrical conductivity, total body potassium, and skinfold thickness measurements, have been used sporadically and with limited success. Therefore, researchers and clinicians continue to seek a BCA method for use in pediatric populations that is safe, noninvasive, easy to perform, comfortable for subjects, relatively inexpensive, reliable, and accurate. With that in mind, Echo Medical Systems is proposing the use of a QMR-based (Quantitative Magnetic Resonance) EchoMRITM system for infants designed to provide the most precise measurements of total body fat, lean mass, body fluids, and total body water of infants weighing from 1 to 11kg. This weight range should be enough for infants up to 12 months, as the weight of a 12-month- old reference boy is about 10.15kg (Heymsfield et al., 2005). The overall aim of Phase I of the project is to validate the precision, accuracy, and effectiveness of the prototype of the EchoMRITM system for infants. Thus, Phase I will entail developing and validating both the 4 kg research prototype and the 11 kg commercial prototype of the EchoMRITM system for infants. After the commercial prototype of the EchoMRITM system for infants (1-11kg) is validated by measuring small piglets during the second year of Phase I, a future Phase II study (not part of this proposal) will then require that the equipment be tested on human infants. The EchoMRITM system for infant BCA will be non-invasive, precise, and safe for pediatric populations, as it will not rely on ionizing radiation. The measurements will be easy-to-perform and exceptionally fast, with a whole-body analysis time of about 5 minutes (including subject prep time).